(x3-2x2+ax+2)÷(x2-4x+1)=x+2
x^3-2x^2+ax+2=(x^2-4x+1)(x+2)
x^3-2x^2+ax+2=x^3-4x^2+x+2x^2-8x+1
x^3-2x^2+ax+2=x^3-2x^2-7x+1
所以 a＝-7